1. Field of Invention
The present invention relates to a magnetic vibrator and, in particular, to a thin magnetic vibrator able to vibrate vertically.
2. Related Art
A conventional vibrator is composed of a rotor with imbalanced weight. For example, as shown in FIG. 1A, the rotor of the vibrator described in U.S. Pat. No. 5,942,833 is composed of a coil 12, a body 10, a holder 9 and other relative elements, and the weight of the rotor is imbalanced with regard to a center axis 8. The stator of the vibrator is composed of a magnet 5, bearings 4a and 4b, a brush 7a and other relative elements. When a current is conducted to the coil 12 of the rotor by flowing through the brush 7a, the magnetic field generated by the current flowing through the coil 12 repels the magnetic field generated by the magnet 5 of the stator. Thus, the repulsive magnetic force drives the rotor to rotate about the center axis 8. Because of the imbalance in the weight of the rotor, the imbalanced centrifugal force and vibration of the rotor are generated during the rotor is rotating. Moreover, the vibration is a horizontal force with respect to the vibrator.
However, the vibration of this type of vibrator can be sensed until the motor is started and then continuously accelerated to reach a certain level of rotating speed; on contrast, after the power is cut off, the rotor cannot stop rotating and vibrating immediately due to the inertial effect, and there is still a sensible vibration effect over a span after the motor is powered off. Thus, the vibrator has a time lag with comparing to the power source or vibrating signal source. Moreover, the vibration force generated by the vibrator is along the horizontal direction rather than the vertical direction with respect to the electronic device or printed circuit board. However, in practice, the users can obviously feel the vertical vibrations stronger than the horizontal vibrations.
As shown in FIG. 1B, another type of vibrator described in U.S. Pat. No. 6,777,895 can generate vertical vibrations and has a vibrating element composed of an outer yoke 4 and a magnet 5. The magnet 5 is hollow annular-shaped, and the direction of the magnetic pole thereof is along the horizontal direction. A stator is composed of an inner coil 2 and an inner yoke 3. When a current is flowing through the inner coil 2, the generated magnetic force and the magnetic poles of the magnet 5 form either a repulsive force or an attractive force for driving the stator composed of the inner coil 2 and the inner yoke 3 to vibrate vertically.
However, there are still some defects in this design. Because vertical vibrations are generated from the vibrating element composed of the outer yoke 4 and the magnet 5, the vibrating element cannot be contacted or held such that a cover 7 is disposed to prevent the vibrations from being impeded. Thus, the size of a whole vibrator is limited, and is adverse for improvement in designing thin vibrators. Additionally, the direction of the magnetic poles of the hollow annular-shaped magnet 5 in this vibrator is horizontal. If the size of the vibrator is too small, the mass production of the vibrator is limited and it is adverse for improvement in designing thin vibrators as well.